1. Field of the Invention
The present invention relates to a flexible, elastic seal adapted to contact a patient's face and create a sealed interface with an airway of a patient, and to a respiratory mask using such a seal.
2. Description of the Related Art
A variety of respiratory masks are known that have flexible seals and that cover the nose, mouth, or both of a human patient. The seal on a respiratory mask, which is also commonly referred to as a cushion, is intended to create a seal against the patient's face. Because of the sealing effect that is created, gases can be provided at a positive pressure within the mask for delivery to the airway of the patient.
The uses for such masks range from high altitude breathing, e.g., aviation applications, to mining and fire fighting applications, to various medical diagnostic and therapeutic applications. For example, such masks are used in the delivery of continuous positive airway pressure (CPAP) or a variable airway pressure to an airway of a patient. Examples of variable positive airway pressure systems include a conventional ventilator, which provides a non-invasive ventilation, a bi-level pressure support system, which varies the pressure delivered to the patient with the patient's respiratory cycle, an auto-titrating pressure support system, which varies the delivered pressure with the monitored condition of the patient, and a proportional positive airway pressure (PPAP) support system, which varies the delivered pressure with the patient's effort. Typical pressure support therapies are provided to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), Cheynes-Stokes respiration, and congestive heart failure.
A requisite of such respiratory masks is that they provide an effective seal against the patient's face to prevent leakage of the gas being supplied. Commonly, in conventional mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort to the patient. This problem is most crucial because such masks are typically worn for an extended period of time. One concern in such a situation is that a patient may avoid wearing an uncomfortable mask, defeating the purpose of the prescribed pressure support therapy.
Numerous attempts have been made to provide a seal that is effective, i.e., provides a seal with the surface of the patient that minimizes leak, and that is comfortable. U.S. Pat. No. 5,243,971, for example, teaches a bubble-type of patient interface in which the seal has a convex surface that engages the user. This patent teaches that the seal is a distentable membrane molded from an elastic plastic material. The convex surface of the seal deforms inward on itself as the user applies the seal on his or her face. It is believed that deforming the seal provides an adequate mask-to-face seal for the application of a positive pressure therapy. It can, thus, be appreciated, that this seal configuration uses the shape of the seal and its ability to deform inward from the original convex shape, in combination with the pressure provided inside the seal by the pressure support system, to provide the necessary seal against the patient's face so that the seal can fit a wide variety of patients, i.e., patient's having different facial sizes and structures.
Rather than rely on the ability of the material forming the seal to deform such that a good seal is created, other seals rely on the type of material forming the seal to create an effective mask-to-patient seal. For example, U.S. Pat. No. 5,647,357 teaches forming the seal from a gel material having a durometer in a range of 20 to 45 on the Shore 000 scale. This type of gel material is very soft to the touch, providing a comfortable interface between the patient and the respiratory mask. The resiliency of the gel material ensures that leaks at the seal-patient interface are minimized. However, these gel cushion are sometimes perceived as bulky or heavy.
Still others have attempted to provide a good mask-to-patient seal through the use of multiple flaps at the patient contacting portion of the seal. See, for example, U.S. Pat. No. 4,971,051. While each of these different types of mask seals may be effective is some patients, there still exists a need for an improved seal for a respiratory mask that is 1) comfortable to wear over an extended period of time, 2) provides a seal that minimizes gas leakage at the mask-patient interface, and 3) fits a wide variety of facial structures and sizes, so that a commonly sized and style of seal can be used on many different patients.